Rats will be fed diets containing 20% of fat with high saturation or high saturation or high polyunsaturation. Cholesterol tracers will be administered and rats will be killed at intervals thereafter for determination of cholesterol and bile acid specific activity in liver and selected peripheral tissues. The data will be analyzed for kinetic parameters and mathematical modeling using the SAAM-27 program will be performed. Other studies will be done using cultured tissue cells. Cholesterol and bile acid kinetics will be investigated.